The invention relates to a differential drive having a differential carrier rotatably drivably supported around an axis in a drive housing. Two axle shaft gears are arranged in coaxial bores in the carrier while being supported so as to be rotatable around the axis relative to the differential carrier. A plurality of differential gears are rotatably supported in axis-parallel cylindrical pockets in the differential carrier and rotate with the differential carrier. A first group of differential gears engage one of the axle shaft gears and a second group of differential gears engage the other one of the axle shaft gears. The axle shaft gears and the differential gears are designed as helical gears. The differential gears, on their tooth heads, rotate with contact in the pockets. The differential carrier consists of a central portion comprising the bores for the axle shaft gears and the pockets for the differential gears, and of two cover parts axially closing the bores and the pockets.
Differential drives of the above type have been offered and distributed for some time by the assignee of this application under the name of "Powr-Trak". The friction forces generated in the helical teeth and axial forces acting on the gears and generated between the teeth due to tooth forces cause increased friction losses which reduce the efficiency of the differential drive and thus increase the locking value. The term locking is used when meaning slip limiting in a limited slip differential. However, to avoid impermissible wear, the friction between the teeth and the end faces of the gears and the cover parts and housing bores must not change into dry friction. Therefore, care has to be taken to provide adequate lubrication. If unfavorable conditions prevail such as long periods where the vehicle is out of operation or if the drive housing contains only a small amount of oil, prior art differentials may temporarily experience dry friction during the starting procedure.
In DE 196 16 807 it is proposed to provide the differential carrier with external pressure agent supply means supplying oil via one of the axle shaft gears, and with additional axis-parallel pockets which extend parallel to, and are provided in addition to, the pockets for the differential gears. These features ensure improved lubrication when starting the vehicle after it has been out of operation for some time. Such external pressure agent supply means, with the oil being supplied through a rotating axle shaft, are disadvantageous in that they have a complicated design.